1. Field of the Invention
This invention lies in the field of fluid flow control valves. More particularly, it is of the type of so-called butterfly valves which are relatively thin in the direction of the flow axis and can be inserted between flanges in a pipeline, whereby the bolts which hold the flanges pass through the body of the valve and clamp it securely and sealably between the flanges.
2. Description of the Prior Art
In the prior art there are a number of patents and other publications describing butterfly type valves for use in the chemical and petroleum industry. Most of these provide an annular valve seat and a valve disc which is supported by the valve stem. The plane of the valve disc is at a selected fixed distance from the axis of the valve stem. The forward face of the disc which seals against the valve seat is usually spherical so that just by turning the valve stem the disc will be rotated from a first position where its plane is in the flow axis to a second position where its plane is perpendicular to the flow axis and its spherical forward surface is in sealing contact with the valve seat.
While these types of butterfly valves are satisfactory for low pressures, the problem of keeping sufficient pressure between the valve disc and the valve seat so as to prevent leakage at very high fluid pressures, without scoring the surface of the valve disc or the surface of the sealing ring during the turning process, is a very difficult problem. In this invention, as in the related patent and application, the valve disc is arranged to be moved parallel to its face away from the seat, before the stem turns the valve disc to open the valve. Thus, there is no sliding contact and no friction between the valve disc and the valve seat while it is being turned, and there can be no physical damage to either the disc or the valve seat by the turning operation. Of course, when the valve is to be closed, it is first rotated so its plane is parallel to the plane of the valve seat and then it is moved horizontally so that any desired force can be applied to the disc to make a seal which will prevent leakage at extremely high fluid pressures.
The feature that is important in this invention as it was in the previously mentioned patent and application, is that one continuous motion of axial translation of the valve stem carries out sequentially the two operations which are needed to open or to close the valve. The invention lies in the features of these two cam mechanisms.